The present invention relates to the removal of contaminants from water by photocatalysis and by adsorption and, more particularly, to the use of ultraviolet-activated titania catalysts to remove both organic and inorganic contaminants from water.
It is known that photocatalytic oxidation using TiO2 can effectively remove organic materials from water. This includes the removal of pathogenic microorganisms and complex organic molecules by oxidation in the presence of ultraviolet light. It is also known to oxidize inorganics, such as heavy metals, by UV-activated TiO2 to change the valance state to enhance removal by other means. For example, arsenic (III) which is difficult to remove from water, can be oxidized to arsenic (V) which is easier to remove by a downstream process such as adsorption.
A method for utilizing photocatalysis with ultraviolet light using a titanium ceramic for the oxidation and destruction of complex organic compounds is described in U.S. Pat. No. 5,035,784 which is incorporated by reference herein. Metal oxide ceramics, including TiO2, can also be formed as supported membranes for use in the photocatalytic oxidation of organics, as described in U.S. Pat. No. 5,269,926, also incorporated herein by reference.
In applying known technology to the practical treatment of drinking water, to remove both organic and inorganic contaminants, there are a number of considerations that must be addressed. The substrate on which the TiO2 layer is deposited should act as a waveguide to distribute the ultraviolet light uniformly through the substrate to activate the TiO2. The substrate material must not only be ultraviolet light transmissive, but should also not degrade in use. The substrate material should also be moldable so that the most efficient waveguide forms may be utilized. Also, the surface of the waveguide on which the TiO2 layer is deposited should provide as large a surface area as practicable within the confines of the size limitations of the apparatus. Finally, the waveguide substrate should also be configured to maximize contact time with the contaminated water flowing thereover. And, of course, the apparatus must be configured to accommodate the ultraviolet light source, typically provided in a tubular construction.